圣诞节即将到来，很多父母都开始为给孩子挑选一份完美的圣诞礼物而发愁。英国心理学家克利夫•阿诺尔最近创制了一个完美玩具计算公式，通过量化玩具价值，帮助家长找到“完美”玩具。阿诺尔把玩具对孩子的作用归纳为“玩乐价值”，计算公式为：“玩乐价值”＝T x L + Pi + Po + Cr + S + U + H /  根号C。其中，Pi代表该玩具在孩子独自玩耍时的有用程度；Po为与他人一起玩耍时的有用程度；Cr是玩具对创造力的启发程度；S代表玩具对社交能力的开发；U为实用性；H为玩具是否可以传给其他兄弟姐妹们玩；T为预计孩子定期玩玩具的时间（小时为单位）；L代表孩子被该玩具吸引的总共时长（以月为单位）；C代表玩具价格。

Parents looking for the perfect toy could use mathematics.

A psychologist（心理学家） has come up with（提出） a formula for parents struggling to find the perfect toy for their children this Christmas.

Dr Cliff Arnall, who has previously¹ come up with calculations for the happiest and most depressing day of the year, reckons（计算，评估） that mathematics can be used to work out the "play value" of potential purchases.

But parents hoping for a simple formula to help them make wise decisions in the toyshop had better not be in a hurry and might have to bring a calculator with them.

The result is also likely to be different for different children, he admits.

Parents first have to assess（估定，评定） the toy against six criteria²（标准）: its usefulness when playing alone (Pi); playing with others (Po); whether it fosters（养育，培养） creativity (Cr); its value promoting social interaction (S); its general utility (U) and finally whether it can be handed down to siblings³（同科，兄弟姐妹） (H).

Parents must give the toy a score out of five for each and add them up.

In a separate sum, then they must estimate the amount of time in hours a child will play with the toy regularly (T) and multiply it by how many months it is likely to remain of interest (L).

The two figures must then be divided by the square root of the cost (C) and added to the total score from the criteria section.

Simple? For those who did not quite follow, it works out as: T x L + Pi + Po + Cr + S + U + H / square root（平方根） of C

"A toy may score higher for one child than another but that's an important part of the exercise," said Dr Arnall.